text:
What happens if a parachute does not open while skydiving?
While skydiving we have to jump from the airplane at a certain altitude above Earth. So if for some reason the parachute doesn't open, then will that person (or any object similar to a human body) fall to Earth or will it be incinerated/vanish in the sky due to air-friction in space before coming down to the Earth?

I'm tempted to give a two word answer to this question after reading only its title: "You die."

@Keavon My question was related to accelerating objects in the space towards Earth. My objective is not to understand whether that person will die or not. How to overcome such situation can be different question for which answer is given by Brian Wheeler here

I was joking, and I said that I wanted to do that after reading only the title.

@Keavon ...... :-)

Interesting read: https://what-if.xkcd.com/28/ in which Randall Munroe investigates whether you can cook a steak with high-altitude drops (you can't)

someone has a very bad day...

Are you not aware that it is very common for skydivers to do extended freefalls at "terminal velocity"?  Thus ruling out "or will it be incinerated/vanish in the sky due to air-friction in space before coming down to the Earth", at least for any normal initial altitude and forward velocity.

The majority of the heat developed during reentry of a space-vehicle comes from air compression not friction. Remember, to go into space, you don't have to go very high, but to orbit you will have to go very very fast, and it's not the fall that produces the heat, it's the slowing down part.
If you had a human fall without a chute, the terminal velocity (where air resistance cancels gravity and you continue downward at a constant speed) would be around 100-200 mph, not nearly enough to cause any kind of heat (or cars would burn up by going normal cruising speeds). To get higher terminal velocities, you'd have to go a lot higher, where the air is a lot less dense, higher than any skydiver have, and as far as I can tell Felix Baumgartner did not experience any incineration during his jump.
The unfortunate skydiver will almost certainly die, but there'd definitely be a body, and it'll probably be in one piece.

I feel the words "reserve chute" should be mentioned somewhere in the answer.

Qualification: I worked at a sport parachute center as an instructor for 10 years and I hold an FAA Master Parachute Rigger certificate. I believe that qualifies me as an expert on the subject.
The fastest a human can fall unassisted is about 300km/h (head-down dive). Far too slow for frictional or compressive heating. Fighter pilots have ejected at supersonic speeds and not warmed up any (it's also rather cold at higher altitudes). You would have to jump from the space station to incinerate yourself.
To answer the primary question, if parachute #1 doesn't open, you use parachute #2. If that doesn't work, you have about 10 seconds left. In consolation, it's not all that messy unless you are unfortunate enough to impact on pavement. An open-coffin service is usually possible.
To reply to other inaccuracies:

the #2 parachute is not spring loaded, the small (1 meter) extraction parachute is.
we don't depend on the idiot box auto-activator. There's a handle.
skydiving in pairs is not "recommended" (that's scuba diving). You want to be very far away from other people when deploying parachute #1, and by then it's far too late for anyone else to help. The close-up videos you have seen are carefully planned in advance - the cameraman and subject agree on relative position and sequence, and the video subject deploys his parachute higher than usual. Videos you may have seen of several canopies together are also carefully planned in advance, and it's a lot harder than it looks.
holding someone else during deployment is not possible. No one is strong enough to hang on during deceleration. It's not (normally) a shock but the forces involved are rather substantial. Backup parachutes DO open very quickly - at freefall speeds it's rather unpleasant.
the exceptionally rare cases of someone surviving without a parachute typically involve a steep slope and either deep snow or crushable foliage. Forget water - at 200km/h it's only slightly more forgiving than concrete.

They sat there is about a 1 in 1000 chance of a primary chute failure, and about a 1 in 1000 chance of a reserve chute failure.  So you typically have about a 1 in 1,000,000 chance of falling to your death during a jump.

@CarloFelicione: It isnt that simple. I heard that most malfunctions are of the type that the primary chute only partly deploys. Then the critical part is getting rid of the primary, which is a prerequisite for safely deploying the secondary. This is where many inexperienced skydivers fail - partly out of psychological reasons because of the reluctance to drop their primary chute. So the two aren't independent.

There is a spring-loaded backup chute that will auto-deploy when the jumper goes too fast and is below 2.5k feet.
If that also fails, the jumper becomes a smear on the ground. Freefall speed (aka terminal velocity) is not fast enough to start any type of burn.

If they are unlucky enough to have a failure to deploy the parachute: They will probably hit the ground at approx 190 Km/h (120 Mph) in one piece. The unfortunate victim will most probably die instantly.

There are occasional stories of chuteless skydivers surviving. Usually they have a partially deployed chute (acting as a brake) and hit something fairly soft. Still, they're injured.

Well, if you skydive in pairs, which as I understand is recommended, and if you catch the error before your partner opens his/her chute, you could signal to them that your equipment is not in working order, and then you could essentially bear hug them while they open their chute.
This is obviously not ideal and could even dislocate the shoulders of the skydiver whose chute did not open.


text:
What would happen to a flying aeroplane if there's suddenly a brick-size hailstorm?
What would happen to a flying aeroplane if suddenly there is hail in the sky?
For example, ice the size of a brick.

you mean if a plane suddenly finds itself in a hail storm?

@ratchetfreak yes..

Hmmm, tennisball-size hail nuggets are the biggest I have seen yet (not airborne at the time, thank goodness). Brick-sized ones? Not good.

It becomes tennisball-size when it come down to Earth, but it must be having bigger in size when it is in the sky.

There is some mass loss to melting and evaporation as hailstones fall, but the bigger ones are falling fast enough they don't have much time for this to effect them greatly.

Right, remember how large hail forms: ice in the updraft accumulates in size until the hail is so heavy that the updraft can't lift it, at which time it sinks to the bottom of the updraft and then falls like a brick of ice dropped out of the sky. As it sinks back through the updraft it is still accumulating ice! Most hail is small because the updraft isn't strong enough to keep lifting it, not because some of the hail turns back into liquid as it falls when it leaves the updraft. It's falling literally like a brick, it's too fast to melt.

The pilot's seat will need cleaning.

Brick. Aluminum. What do you think will happen?

@AmitG Why do you want to know

http://www.airliners.net/aviation-forums/general_aviation/read.main/5919504/

Depends on the aircraft, but take a wood and fabric covered aircraft as an example... a house brick sized hailstone isn't going to do it any good, that's for sure.

It depends on the severity of the hailstorm. In the event of encountering large hail pieces in the sky during cruise, a pilot will generally try to climb above the storm (of course with ATC permission) to prevent damage to the airframe. However, it is always better to stay out of the hailstorm in the first place and pilots will usually try to negotiate a course avoiding the hailstorm entirely using available weather data.
However, there are much more extreme cases such as this Boeing 727 which cracked its radome and its windshield after flying through a hailstorm at FL 350:

There were no pax onboard as it was a cargo flight for Capital Cargo International Airlines. After the severe damage to the airplane, the crew declared an emergency and safely landed at a diversion airport. Surprisingly, the airframe was repaired and put back in service after the incident.

I don't think it's too surprising this was repaired. Radome is not pressurized so it's easy repair, windshields are also replaced quite regularly and there does not seem to be bad damage to the structurally important parts.

Surprising because on such an old 727 airframe (in 2006!), you might want to just retire it instead of funding the future exorbitant maintenance expenses :)

A southern airways flight had a flameout and attempted to land on a highway but hit a gas station after flying through a thunderstorm with lots of hail.

They were trying to fix the flame out issue by adding flame?

There was a case where an easyJet Boeing flew through a hailstorm; the accident report is here, with a PDF download available, which lists some of the damage (which includes a cracked windscreen and damaged leading edges on wings and other surfaces).
There are photos showing the damage incurred, including the one below. Search for "easyJet hailstorm damage" to find more.

Bugger! And those sure were not even brick-sized...

Frozen precipitation comes in many forms

Hail
Graupel
Sleet
Snow
Freezing rain (technically supercooled and not frozen)

Of these, hail and freezing rain are the biggest threats to aircraft and I'll focus on hail as that seems to be the topic of your question.
Hail, especially "brick sized" hail require very strong updrafts in severe thunderstorms to be able to form. We typically name hail sizes by round objects (not bricks) and on the high end we have baseball and softball sized hail. Hail bigger than that does exist, but it is uncommon.
These bigger hailstones are almost exclusively found very close to the updraft in supercell thunderstorms. To encounter these you really need to be flying somewhere you should not be. The turbulent conditions that will exist in the region of these hailstones is already a large threat to an airplane. Hailstones this big will severely dent the fuselage and likely shatter the windscreens. It would be a significant event. However these hailstones don't appear out of nowhere and you are extremely unlikely to see one if you aren't penetrating the worst part of severe storms.
Smaller hailstones can be further from the updraft of a storm and can be lofted some distance in the anvil (which extends downwind for many miles) in certain conditions. Here we are considering golf ball sized hail and smaller, which are still confined to being associated with thunderstorms. These hailstones will dent the aircraft skin and can possibly damage the radome and windscreens.
Most examples of hail damage you will find are aircraft that were on the ground as storms passed overhead.
You won't find "brick sized" hail randomly in the atmosphere, and you should not be getting close enough to experience these if you're flying safely around thunderstorms.
Here is an image courtesy of NOAA (public domain):

This image depicts composite radar (on the "ground" in the image) and a vertical radar cross section through the storm. The area labelled "Hail Core" is where the very large hail is going to be formed and is falling. The extreme radar echoes in this area are entirely due to the extremely reflective properties of the hail. This is an area of intense downdraft due to the falling hydrometeors. The area labelled "Weak echo region" is the base of the updraft. It has a weak radar presentation, because it is fast and violent enough that vapor is not condensing and raindrops not forming until well above the ground, and it is the raindrops and larger objects that radar can show us. Hail or no hail, this is not a region you want to be flying an airplane into.

Hey, is Graupel an English term? Anyway, I can confirm that even slight hail makes for a very uncomfortable feeling :D

@yankeekilo The word is german in origin.  It refers to an ice aggregate that has not experienced a melting/freezing cycle and lacks a solid ice core.  It is a precursor to hail, but sometimes precipitates without becoming hail.

in other words if you have brick size hail impacting you plane then you have a bigger problem with the winds accompanying them

@ratchetfreak see my edit, I added a picture to demonstrate.

One thing to watch for is that hail can be blown downwind from the storm when it is "spit" out the top of the thunderstorm, so stay away from that area too!

Most of what I know has been mentioned, and excellent photographs!
When ice and water go into the air intakes of the jet engines, the ice gets rapidly chopped up into tiny pieces -- those spinning things you can see in the front of the the engine are turbines that slice and then compress the air going through, so the engine has more air to burn with, which generates more energy. It burns, and the exhaust comes out the back. At the back, the exhaust spins the whole turbine assembly, more air goes in, and so forth.
I've talked with SR-71 Blackbird pilots who tell me "essentially nothing" happens if a bucketload of ice and snow goes into those engines.
The things to actually watch out for are, first, as mentioned, impacts, and second, more subtly, is ice can form on the wings. The ice screws up the shape of the wing ("airfoil"), and that shape is what generates lift. Too much icing can make a plane fall out of the sky.
The planes generally do have anti-icing measures -- mechanical, electrical heat -- and this is why the wings and cockpits are sprayed with de-icer before they back away from the gate when it's cold.
That helps some, but if you encounter wing icing, it's best to turn around and land, and call it a day!

those engines are tested to have essentially a firehose aimed at the intake and still run fine

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Do Air Traffic Controllers have to remember stall speeds for different aircraft?
While dealing with Takeoffs and Landings controllers provide speeds to pilots for different phases of the flight, specially during a landing approach.
How do they know which speeds are safe for all the different models operating to and from their airport? Are they provided with that data daily or they have to remember those speeds?
If a general answer is not possible I would be more interested in knowing about stall speeds during a landing approach. Obviously they will be different for different aircraft in different conditions.

ATC doesn't actually assign landing airspeeds. They simply clear them for the approach and from then it's up to the pilots to establish the appropriate landing speed for their aircraft. Further back in the descent or cruise, ATC may issue a speed restriction, but that is never low enough to come close to a stall.

Don't they say Reduce speed to X Knots?

If they need to slow them down (or sometimes speed them up) for traffic purposes, yes, but that falls under the last sentence in my comment. But if there is no traffic, usually they just let the pilots manage their speed themselves. Pilots do not need a clearance to change speed, unless ATC has asked them to maintain a specific speed.

I see. Thanks for that!

No because aircraft are categorized by their speed at the runway threshold (1.3 times stall speed).

VAT —Speed at threshold used by ICAO (1.3 times stall speed in the landing configuration at maximum certificated landing mass)
By knowing the category, ATC is able to use appropriate speeds. The category is not actually listed anywhere, so the controller will have to know the approach category by heart for each aircraft type. E.g. if the controller sees "B738" as the aircraft type in the flightplan, they have to know that the corresponding approach category is C.
More:

ICAO Doc 8168 PANS-OPS Vol 1
14 CFR Part 97.3 (for the US)

@HankyPanky The pilot might also refuse a speed command by saying "unable".  ATC would then need to adjust their plan to accommodate.

I see, thanks Simon!

I think the point was that the pilot in command is responsible.  If the concern is that ATC would inadvertently cause an aircraft to stall the PIC would still be held responsible.

What to do if an aircraft has a V-AT above 210 knots?

@Sean: "What to do if an aircraft has a V-AT above 210 knots?" When a new problem arises, we adapt our practices. Not a big challenge here, we could create a "F" category. In the meantime, or if for some reason a pilot needs to approach or land at an abnormal speed, the crew and ATCO can still agree on this speed. Categories are only a mean to speed up this discussion.

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How much leverage do commerial pilots have on cruise speed?
If you fly frequently there are chances you have seen some delays in departure  where you end up waiting in the aircraft sometimes for multiple hours.
Almost every time that happened I remember the PIC announcing something in the lines of We will try to make up for the lost time...
And they manage to do a very good job at that. One of my recent flights was delayed 2 hours on departure but arrived only 1 hour late.
Its quite exciting when they say that, its like wow he/she will speed up! but how much leverage do they have to accomplish that? I'm sure there are commercial as well as regulatory requirements to remain within a range but how broad that range is for general commercial aircraft?
The aerodynamics and engineering part of this problem I know about, I'm mostly interested in the commercial aspect of it. Are the speed ranges set by commercial interests?

Most of the made up time comes from luck: Flying in a tailwind for hours has by far the biggest impact on travel time.

Thanks! normally its always the case. But in this specific case it was headwind and still they managed to save some time

I suspect most of the time they "make up" is due to a buffer that was actually included in the schedule from the start and some help from the ATC like direct clearance and vectors to shorten the departure and approach.

Related: How can an airliner make up for time lost?

I heard a better one recently: "We will make up for this lost time in flight." (of course, the delay was only ten minutes...)

Related on Travel Stack Exchange: Delayed plane: Why is the delay on the departure time larger than the the delay on the arrival time?

There is something called the "Cost Index" - it is basically how you choose between speed and fuel economy. Company dispatchers, after knowing that a flight has been delayed, will calculate this value, and the pilots simply input the updated value into the FMC (Flight Management Computer). That will instruct the autopilot to output more thrust, i.e. fly faster, but less fuel efficient.

Related (not a duplicate): What is Cost Index?

In addition, they can request a more direct routing.

The dispatchers also may be able to find an alternative route that is not more direct but has better tailwinds. But notice that "we" is not just the flight crew; there are things a dispatcher can do to reduce flight time that the pilot would not be authorized (or even have the ability) to do on his or her own.

It might also be worth mentioning that the added cost is only worth it when compared with the cost of a delayed flight (with e.g. a bunch of passengers to re-route and so on), which is strictly out of the hands of the pilot in command.


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How does my Casio watch know the altitude in flight?
Wrist watches usually use the barometric pressure sensors they have to calculate the altitude. I have also confirmed this from the manual of my watch, which states that:

The watch displays altitude values based on air pressure readings taken by a built-in pressure sensor.

Fine that's understood and makes sense and has always worked for me wherever I go.
Question
But then how does it know altitude during flight? The cabin of all commercial airliners are pressurized and hence the air pressure is not changing inside the cabin with the change in altitude (as happens for descent or ascent on ground). I know that even the aircraft itself uses pressure sensors for many calculations but those sensors are mostly usually on the Pitot tube and they sense the real outside pressure and not inside an pressurized cabin
I would also like to mention that yes the altitude reading it takes during a flight is not always close to what the real value is but still it does track the altitude difference when pressure inside the cabin remains same, how so?
Please note
That I didn't include the exact details of my watch because neither am I promoting any special model or a brand nor am I asking specifics of how a watch works, focus is on air pressure inside the cabin, not on watch. If needed I can provide the model and manual reference links.

But you should be more specific regarding what value it shows.

The pressure inside the cabin does NOT remain the same.  That's why you need to equalise the pressure in your sinsuses, usually during descent.  Your watch will be showing you the cabin altitude, probably somewhere around 2500 metres.  Pitot tubes are not used to measure static pressure.  They are used to measure dynamic pressure and calculate airspeed.

This may be interesting for you, too: What's the relation between cabin pressure and altitude?

I assume your watch doesn't give an altitude reading above 10,000 feet or 3,000m, whereas a typical commercial flight cruises at over 30,000 feet or 10,000m. That means it shows the cabin pressure (which isn't constant) rather than the correct outside pressure.

@tas that is correct

The pressure in the cabin does not remain the same. It decreases, but much more slowly, in such a manner that when the aircraft is at 37000 feet the pressure in the cockpit is the equivalent of 7000 or 8000 feet. Keeping the cabin pressure at sea level would pose incredible stress on the fuselage, due to huge difference in pressure between the inside and the outside.

This note by Boeing can substantiate this answer: Today's airplanes are pressurized to a typical cabin altitude of 6,500 to 7,000 feet (1,981 – 2,133 m), with a maximum certification altitude of 8,000 feet (2,438 m). http://www.boeing.com/paris2013/pdf/BCA/bck-787%20interior.pdf

"incredible stress on the fuselage" -- to be clear, do common planes have a hypothetical failure mode in which the plane fails to release pressure during ascent and the fuselage ruptures? By "hypothetical" I suppose I mean it's realistic, it is what would happen if pressure weren't released, but some kind of fail-safe doohickey no doubt would prevent that by blowing out first even if the normal systems failed to let any air out.

@SteveJessop: Yes, normally the system incorporates valves that will open if a certain pressure differential is reached (positive or negative). There should be at least two such valves and only half of them should be enough to keep the pressure difference between safe limits.

Like most things, there is some fail safe redundancy built in just in case the valves all fail.  On some types, there are "frangible" panels or burst discs which will blow out to equalise the pressure.

Doesn't the 787 Dreamliner pressurize to a higher degree on account of its carbon fiber fuselage?

@RoboKaren See this note from Boeing: Because the advanced composite materials that make up the 787’s fuselage do not fatigue, the 787 can be pressurized more, which allows for lower cabin altitude levels.


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Are you allowed to do your entire PPL on a medium-sized jet aircraft from day one?
I'm wondering if say, hypothetically, I had a friend who had a large aircraft (e.g. Learjet), could I do my PPL hours on it from day one, or is there anything stopping this?

It will not work in EASA for a variety of reasons. Of the top of my head:

Like Lnafziger mentioned, you will need to do at least 10 hours solo. Most jet engines (but the smallest such as the D-Jet) have a minimum required crew of two. Also, you are not allowed to switch airplanes in the PPL course (ie. fly solo with one airplane and dual with another see FCL.235) so you are stuck.
Most jet aircraft (and as far as I know all commercial ones) are multi-engine. You will need 70 hours PIC before you can receive instruction on multi-engine, and you cannot fly PIC before you have your PPL.
Multi-engine jet aircraft require a type rating, which has a lot of license pre-requisites before you are even allowed to enter the cabin: MCC, IR, MEP(land)

There are a few prerequisites specified in  Part-FCL about getting your first class or type rating, and to accomplish most of them you will need to have at least a PPL (eg IR(A), ATPL theory tests, hours PIC ,etc)

FCL.235 Skill test
(b) An applicant for the skill test shall have received flight instruction on the same
class or type of aircraft, or a group of balloons to be used for the skill test.
FCL.720.A Experience requirements and prerequisites for the issue of
class or type ratings — aeroplanes
Unless otherwise determined in the
operational suitability data established in accordance with Part-21,
an applicant for a  class or type rating shall comply with the
following experience requirements and prerequisites for the issue of
the relevant  rating:
(a) Single-pilot multi-engine aeroplanes. An
applicant for a first class or type rating on a single-pilot
multi-engine  aeroplane shall have completed at least 70 hours as PIC
on aeroplanes.
(b) Single-pilot high performance non-complex aeroplanes. Before starting flight training, > an applicant for a first class or
type rating for a single-pilot aeroplane classified as a high performance aeroplane shall:
(1) have at least 200 hours of total flying experience, of which 70 hours as PIC on aeroplanes; and
[...]
(c) Single-pilot high performance complex aeroplanes.
Applicants for the issue of a first type rating for a complex single-
pilot aeroplane classified as a high performance aeroplane shall, in
addition to meeting the requirements of (b), have  fulfilled the
requirements for a multi-engine IR(A), as established in Subpart G.
[...]
(d) Multi-pilot aeroplanes [...] or comply with the following
requirements:
(1) have at least 70 hours of flight experience as PIC
on aeroplanes;
(2) hold a multi-engine IR(A);
(3) have passed the
ATPL(A) theoretical knowledge examinations in accordance with this
Part; and  [...]

sensible suggestions, thanks :)

Oddly enough, EASA has a different understanding of 'complex' (see http://aviation.stackexchange.com/questions/1258/what-are-the-requirements-for-a-complex-airplane )


text:
What security clearances does a foreign citizen doing a flying course in the United States have to pass?
I remember reading that the security for foreigners doing a flying license in the United States were rigorous (as would be expected). As a European Union citizen, what would I expect to need to do from a paperwork/legal standpoint (FAA, CBP etc.) to be allowed to pursue a private licence in the USA, assuming I have no previous flying experience?

@casey Specifically thought that there might be a few countries like the EU ones with less restrictions, but in that case i'll rephrase my question :)

While technically you didn't ask this,  may I point out that Canada will allow an EU citizen to obtain a PPL without any kind of visa at all. There are questions on the Travel site about it.

See also: http://travel.stackexchange.com/questions/8400/where-can-i-combine-a-vacation-and-learning-to-fly-with-a-tourist-visa-rather-t

@DJClayworth thanks for the tip, will take a look :)

You need 2 things before you can start flight training in the U.S.:

An appropriate visa. A tourist visa (B2), business visa (B1) or VWP (Visa Waiver Program) is not accepted
TSA clearance through the Alien Flight Student Program (AFSP)

The complete process is documented at the AOPA website.
In a nutshell, this is what you need to do:

Make sure you have a proper visa or permanent resident card (green card). A visa that allows you to live in the U.S. is fine (you don't need a specific visa for flight training). Examples of appropriate visas: H1B, H4, L1, L2 but there are many others
If you don't have one of the visas mentioned above, you need to apply for a student visa (M-1). You need to contact a flight school that will assist you with the visa application.
Contact a flight school if you haven't already done so in the previous step. They will register your "case" and provide you with information you need when applying for TSA clearance.
Apply for the AFSP program on the TSA website
Wait for approval by the TSA (is a multistep process that could take a while. It includes having your fingerprints scanned, among other things)
Start your training

You should first find the school, then start to take care of the TSA procedure (as it takes a lot of time) and then get your visa. You need an I-20 form issued by your flight school in the US to apply for your student visa.

Ok, you're right. I changed my answer to reflect that. But this is only true if you want to apply for a student visa just for flight training. It doesn't apply to green card holders and people already on a appropriate visa (H,L,...)

TUnfortunately I don't have any experience with holding a green card and so do most other europeans. Anyway getting the appropriate visa takes only a few days so it meight wait and should not stop you from doing all the AFSP steps which can take moths. I would suggest to Find an experienced school first. They will help you with any further steps. Next would probably be to take one day at the computer and initiate all the other steps. Sign in for AFSP, book your flight, organise an apartment and apply for your required visa.

Can you please give me a reference for your first point in a nutshell? (A visa that allows you to live in the U.S. is fine Examples of appropriate visas: H1B, H4, L1, L2 but there are many others)

There are two different legal requirements for a citizen of a foreign country to do flight training in the United States:

You require an TSA approval for each course you intend to participate in (if you for example also like to do your instrument rating in the US you need a second approval). Read more about TSAs Alien Flight Student Program on their website
You're also required to have a visa to legally stay in the United States for the time of your training. Most probably you'll require a student visa (M1) but maybe also another type of visa is appropriate for you. Find more information on the website of the US embassy in your country.

When choosing your flight school do not only consider getting the TSA approval but also if your flying hours there will be accepted by EASA to get your desired license.


text:
Why is there a difference between nosegear retraction directions?
I've noticed that on almost all aircraft (Boeing, Airbus etc.) the nose gear rotates forwards for retraction.

However, on a some aircraft, in particular a few Russian models, the opposite is used: the nose gear is rotated towards the rear for stowage:

(this includes the Tu154, Tu134)
Is there any logic behind this decision? I imagined it was better to place it folding forwards, such that the gear was assisted into place by the air, especially for manual free fall. Looking at pictures of the TU-154 with its gear down, there seems to be plenty of space forward.

You've really answered your own question.  Forward retracting gets significant assistance from drag in a free-fall release; space - retract rearward on many types = less cargo space; legacy (I suspect - think Boeing vs Airbus tail and stabiliser configurations).

Apart from everything else, retracting back is just more beautiful :)

For both main and nose landing gear the main and really only consideration is where they can make space for the gear (there is no standard direction for retracting the main landing gear either; the Tu-154 retracts main gear rearwards into the anti-shock body).
The most common configuration is retracting nose gear forward, because it's easy to make space for it there leaving more space for the cargo hold. I don't think the air pressure during gravity extension plays any role in the decision.
Most older Russian planes were however originally designed with glass nose seating navigator, so they did not have the room there. It was no longer the case with Tu-154 though. So they either had other equipment there or were simply used to making it retract rearward and didn't think about the advantage of changing it.
The most common configuration for main gear is retracting it inward into the wing box, but note that the Tu-154 is exception there as well retracting the main gear into the rather large anti-shock bodies. Because they needed the anti-shock bodies they thought how to use them and there were not that many options.

finally got a logical explanation with that navigator position, thanks :)

It is not really fair to say that "they needed the anti-shock bodies" and so "they thought how to use them". Tu-154 "needs" them just like any other airliner, and they could have been implemented differently. In reality, they were first designed for Tu-16 explicitly as landing gear bays but yes, with the 'area rule' in mind. Then this design was inherited through Tu-104, 124, 134 (which were direct derivatives of Tu-16) to Tu-154, which was, although an all-new civil design, still the same school of thought.


text:
Are there any speed and altitude limitations on the autopilot?
This comes from a flight simulator experiment ages ago in the Boeing 737....

I'm on the runway. I engage the heading switch, followed by the altitude and thrust. The aircraft lifts off, although hardly in a clean rotation.

Now I'm wondering: While it did work in the flight simulator, will the autopilot follow these commands in real life as well if I  repeated this in a business or commercial jet?
Is there anything stopping the autopilot from engaging a specified altitude or from following instructions which are utter nonsense?

I doubt it will go below stall speed unless in a landing configuration and close to the ground

@ratchetfreak: The autopilot will attempt to do whatever you tell it. The stick shaker should disconnect it though.

It depends on the autopilot and you need to read the AFM to know what the limitations are.
All of the business jets that I have flown prohibit the use of the autopilot below a specific altitude (between 50 and 1,000 feet depending on the autopilot and the configuration of the airplane). Nothing prevents then from being used lower but it isn't allowed.  They will engage on the ground (in fact it is part of the required preflight tests) but have a specific prohibition against use for takeoff and landing.
Other airplanes and autopilots however are approved for autoland all of the way down to a full stop, and some for takeoff as well.
Speeds also depend on the autopilot.  Some automatically disconnect if the aircraft receives a stall warning or overspeed signal but others don't.

As I remember, the two 747 carriers I worked for had statements in their op specs that prohibited the use of autoland. The aircraft still had the capability (which we occasionally played with), but neither carrier was willing to incur the costs of maintaining autoland capability or training for it.


text:
Are GPS airspeed meter and altimeter going to replace traditional measurements?
When are GPS Airspeed meters and Altimeters going to be introduced if they not already in use?  Are they more accurate than systems in use now and? How much would it cost to install them to older aircraft?

How do you propose GPS would be used to measure airspeed?

Related: https://aviation.stackexchange.com/q/29154/520

In general, even very low cost GPS units can provide very very accurate velocity vectors.
Altimetry is not quite as good, and is different in that it is referenced to a geoid, rather than a barometric pressure.
Similarly, airspeed is referenced to the ambient air, and while a GPS is a very accurate velocity vector source, there is no easy way to know the ambient air velocity.
So in short, by necessity to maintain safe flight, airspeed utilizes relative wind on an aircraft, and there is not an easy way to determine that with GPS alone.  And altimeter settings by convention, are based upon ambient air.  However, by utilizing a geoid model reasonably accurate absolute altitudes or MSL altitudes could be determined. Cost? As much as an old cellphone and some software.  Pretty cheap.

Except that if using GPS for these types of instrumentation, the costs aren't going to be cheap. The system will still have to be certified in the aircraft, and an old cell phone and some software isn't going to cut it.

Geoid, in the sense that the altitude information for aircraft is conventionally referenced to MSL.  If functioning as an analog to a radar altimeter then the answer is different.    With respect to costs, I did not speculate on the certification costs, and the avionics manufacturing costs, as that would obscure the fundamental low cost of the underlying device.

Based on my experience with using GPS to estimate altitude in cycling, the pilot who relies on such a device will soon be a dead pilot.

I take it your cycle GPS is not WAAS enabled (grin).


text:
How does the F-35's roll posts work, and how does its engine turn down 90 degrees?
I've heard about the F-35's roll posts but I don't get how they work and how its engine turns downwards 90 degrees, any ideas?

Relevant.

Expensively....

The mechanics of rotating nozzle is actually identical to the adjustable angle of a cheminy pipe: https://www.google.com/search?q=sheet+metal+chimney+elbow&source=lnms&tbm=isch&sa=X&ved=0ahUKEwixssjxy4TWAhVp6oMKHQx-An4Q_AUICygC&biw=1200&bih=1811#imgrc=7cQS3QP69zIK0M:

The purpose of the roll posts is to let the pilot have some control authority in hover and stabilization, along with controlling aircraft attitude. Basically, the Rolls Royce Lift System used in the VTOL F-35 has three components connected by drive shaft (along with the engine):

The LiftFan at the front
Three-bearing swivel module (3BSM), which turns the nozzle through 95$^\circ$, and
Two Roll posts on either side of the fuselage.

F-35 Liftfan system; image from nationstates.net
Basically, some bypass air is directed towards the (individually adjustable) roll post ducts to ensure stability during hover, which is done by the onboard computer. In this image, you can see the roll post doors opening on outboard sides of the MLG doors.

F-35 roll post doors opening; image from nationstates.net
The 3-Bearing Swivel Module (3BSM) has three segments driven by two actuators (the first one drives the first segment, while the second one drives the second segment directly and the third one through an angle gearbox). The three segments are cut at an angle, so that when transferring from forward flight to hover, the central segment ends up with its longer edge at the top (so that their sections with maximum length are on the same side), thus 'summing' the bearing offset angles to give a 95$^\circ$ deflection of the jetpipe nozzle in the downward direction.
From codeonemagazone:

The three-bearing swivel nozzle, 3BSN, design uses three segments of the engine exhaust duct cut on an angle and joined by two airtight circular bearings. External motors drive geared teeth in these segments to rotate them to create the deflected thrust. The forward and aft segments always stay aligned with one another in the rotational axis. The center segment rotates through 180 degrees relative to them. The third bearing is on the back of the engine aft of the turbine stage and provides the ability to swivel the nozzle thrust axis in yaw at any pitch angle.

Three bearing swivel module, from codeonemagazine

I was going to flippantly answer this question with "magic," but I decided not to, because there's clearly good scientific answers like the one you provided.  However, after reading it, I'm starting to think my "magic" answer isn't as far off the mark as I'd originally thought.

For a mundane example of the swivel duct, visit your local Home Depot - in the plumbing and heating section. Elbows for forced air ducts are built around the same idea, although in that case, it's for a fixed installation.

"Any technology that is distinguishable from magic is insufficiently advanced."  I may have mangled that quotation.


text:
Who can perform different maintenance checks?
The different types of check (A-check to D-check) require different types of competence and certification.
If I understand correctly, D-checks require special equipment and certification and some airlines developed whole subsidiaries to take care of this task (LHT, AFI,...) in which they send their aircraft to perform a D-check.
Given the existence of those subsidiaries, I assume that a D-check cannot be performed by the airline's employee and must be performed by a company specialized in aircraft maintenance.
A-checks and daily maintenance do not require the same amount of qualifications, certification and equipment and may thus be performed by the airline without sending the aircraft to a specialized place.
For each check (A-check, B-check, C-check and D-check), who is qualified to perform those checks? Can these checks be performed by the airline itself or must a specialized company take responsibility for the aircraft?

Not a full answer, but in reply to your last question, it doesn't matter who does the work, the airline is still responsible for the maintenance and the aircraft as a whole.   That responsibility can not be delegated..

Airlines are free to conduct the tests wherever they prefer as long as they meet the required FAA standards.
An extract from American Airlines' Procedures:
"PS" Daily Checks
Each aircraft is checked every 2-3 days in its "PS" (Periodic Service) check. The aircraft is visually inspected and its maintenance log book is checked for entries and maintenance needs. The "PS" check can be performed overnight or during downtime during the flight day. It averages approximately two manhours.

"A" Checks
The "A" check is more detailed than the "PS" check. "A" checks are performed every 7- 9 days (approximately 80 - 100 flight hours). The "A" check is performed at one of 40 stations around American’s system. It averages 10 - 20 man-hours.

"B" Checks
The "B" check is an even more thorough maintenance check. The "B" check is accomplished approximately every two months (roughly 500 - 600 flight hours). Besides specific service performed on the aircraft, a detailed series of systems and operational checks are performed. American always performs "B" checks inside one of its hangars at seven different cities around its system. A "B" check requires approximately 100 man-hours on narrowbody aircraft (those with only one aisle) and approximately 200 - 300 man-hours on widebody aircraft (those with two aisles).

"C" Checks
The "C" check is the most thorough type of maintenance work performed by American. The airframe - virtually the entire aircraft - goes through an exhaustive series of checks, inspections and overhaul work. It is performed at either of American’s heavy maintenance and engineering centers in Tulsa, Oklahoma or the Alliance Maintenance Facility in Fort Worth, Texas. There are different levels of "C" checks depending on the type of aircraft.

Jet Engine Overhauls
Modern jet engines are among the most reliable devices in aviation. American does not replace and overhaul jet engines at a specific number of hours. Instead, American uses a 24- hour-a-day "condition monitoring" process that scientifically tracks the condition of every engine on every aircraft. Besides visual inspection, technicians monitor the internal condition of every engine, using such procedures as boroscope inspections and oil sample spectographs. The goal is to replace and overhaul an engine before a problem can occur. Engine overhauls are performed at the Tulsa and Alliance-Fort Worth Maintenance and Engineering facilities. The engine replacement is usually performed at one of the six "B" check hangar locations around the country.

To answer your question on the qualifications required to perform these checks, we'd have to go to FARs Part 65 which lists the privileges and limitations of a Mechanic Certificate.
In addition to the basic Mechanic Certificate, FAA allows two different ratings.
The first one is the Airframe Rating which, under §65.85, states:

A mechanic who holds an airframe rating may approve and return to
  service an airframe, an appliance, or any related part after he or she
  has performed, supervised, or inspected minor repairs or alterations.
  He or she may also perform the maintenance actions required for a
  major repair or alteration, and should initiate the appropriate form
  (FAA Form 337, Major Repair and Alteration) associated with that work.
  However, the return to service action must be accomplished by a
  certificated A & P technician holding an Inspection Authorization
  (IA). (Refer to 14 CFR §65.95.)

After that comes the Powerplant Rating under §65.87 which states:

Similarly, a mechanic holding a powerplant rating has the same
  limitations imposed regarding the powerplant and propeller as the
  airframe technician has on the airframe rating. He or she may perform
  and return to service minor repairs or alterations. He or she may also
  accomplish the work activities required for a major repair or
  alteration, but the work must be signed off for return to service by
  an IA.

That said, after all the checks have been performed, a person with Inspection Authorization (under §65.91) is responsible to approve the aircraft for return to service.
Source: American Airlines Aircraft Maintenance Procedures Fact Sheet

And all are bound by the mechanic's creed

Can you provide some sort of source identification for the AA procedures you've quoted? A link to an on-line source, or the official name of the document that others may be able to get to? (I realize that this may be an internal document - do you work for AA?)

@FreeMan Sure, sir. Edited and added the source. Thanks.


text:
Why do newer commercial aircraft have their wingtips curved up?
Lately I've seen a lot of aircraft that have the wingtips curved up.  What is the reason for this?

related http://aviation.stackexchange.com/questions/8544 and http://aviation.stackexchange.com/questions/8556

Presumably because with composites, they can. Curving aluminium or steel would be a lot harder. With a composite wing, you can lay down the fiber in new ways.

Hey, Scottie. Just wanted to let you know that I'm closing because there is already a duplicate – with very different wording – not because it is a bad question (it's not!).

I think we shuold leave this question here.  It's a good example of this question on meta.  Some people might now know what winglets are, so this question will lead them there.

For drag reduction, due spilling air from the underside of the wingtips  over the top side where the pressure is lower.After that the swirling pattern of airflows is left behind. So to minimise but not eliminate them the winglets is added


text:
Why are some ATC call signs different than the flight number?
When listening to air control traffic, or watching flights on flightradar24.com, some flights show up with ATC call signs (as transmitted on ADS-B) that do not match the flight number as they usually do, some examples:
TK1880 / THY9QT
TOM6347 / TOM1FT
LH1660 / DLH5KK

It seems to be more frequent on flight codes that have 4 digits, but this isn't exclusive. Who assigns these call signs, and what is the pattern for the naming?

This is common practice outside the US, I believe the purpose is to keep call signs easily distinguishable. Call signs with just numbers have a tendency to get transposed and mixed up.

It's worth noting that DL is an ITU call sign prefix for Germany. If LH is shorthand for Lufthansa, that makes sense.

Related: How is an airline call sign assigned?

Related: http://aviation.stackexchange.com/questions/8767/when-do-we-use-iata-codes-and-when-do-we-use-icao-codes

In addition to the confusion problem explained in the answers, the ATC ID (ICAO code) cannot be paired with the IATA ID in at least two cases. 1/ The same aircraft carries passengers for two IATA flight codes (e.g. two airlines sell the same flight under their own code and then charter the same aircraft). 2/ Two aircraft in flight at the same time for the same IATA ID (e.g. a departure every 2 hours, flight time is 90 minutes, but the first aircraft is delayed one hour).

@user: LH and DLH are the IATA and ICAO codes both for Lufthansa, respectively.

Who assigns these callsigns, and what is the pattern for the naming?

Callsigns are allocated by ICAO. Their Annex 10 Radiotelephony Procedures says

5.2.1.7.2    Radiotelephony call signs for aircraft
5.2.1.7.2.1    Full call signs
5.2.1.7.2.1.1    An aircraft radiotelephony call sign shall be one of the following types:
Type a)   —   the characters corresponding to the registration marking of
  the aircraft; or
Type b)   —   the telephony designator of the aircraft operating agency,
  followed by the last four characters of the registration marking of
  the aircraft;
Type c)   —   the telephony designator of the aircraft operating agency,
  followed by the flight identification.
Note 1.— The name of aircraft manufacturer or name of aircraft model
  may be used as a radiotelephony prefix to the Type a) call sign above
  (see Table 5-1).
Note 2.— The telephony designators referred to in b) and c) above
  are contained in ICAO Doc 8585 — Designators for Aircraft Operating
  Agencies, Aeronautical Authorities and Services.

In the case of TOM6347 / TOM1FT,
Flight Number:         TOM6347
Aircraft Registration: G-CPEU
Aircraft type:         B752
Callsign:              TOM1FT

As Jamiec commented, TOM1FT 'matches "C" - 1FT is the carrier-allocated "flight identification"'
I guess the use of alphanumeric flight identifications may be due to the 7-character limit on ICAO callsigns, the use of 3-character ICAO prefixes, the use of single-character suffixes (e.g. for delayed flights) and the need by large airlines for more than 1000 flight numbers - Reference
Flight Identifications can be changed when two or more flights with similar flight numbers fly close to each other.

It used to be that ICAO specifications had no force in regulation but were merely suggestions. Is that still true?

@Terry: That would make a good question!

@Terry seeing as the UN (which hosts the ICAO) has no legal authority anywhere to make laws, yes. Of course many countries will adopt the ICAO recommendations and turn them (or use them as basis of) their own laws. But it's effectively an advisory body.

IATA and ICAO has different methods of specifying flight designators. For IATA:

A flight designator is the concatenation of the airline designator, xx(a), and the numeric flight number, n(n)(n)(n), plus an optional one-letter "operational suffix" (a). Therefore, the full format of a flight designator is xx(a)n(n)(n)(n)(a).

ICAO on the other hand, calls for:

the ICAO designator for the aircraft operating agency followed by the  flight identification... when in radio telephony the call sign to be used  by the aircraft will consist of the ICAO telephony designator for the operating agency followed by the flight identification

There is no rule that I'm aware of that says that their identifiers should be the same. Flight plans use ICAO codes for flight identification, while IATA codes are mostly used for ticketing and other commercial purposes. It is entirely possible that the same aircraft has different codes, usually to avoid callsign confusion, as the ICAO callsign is sued for ATC purposes.
That being said, this seems to be mostly used in Eurpoe, rather than US (all the flights you've given as examples are from Europe). From this forum:

... In North America the airlines only add a letter designator to a flight number if a flight with the same number is in the air at the same time; which is a rare occournance.
On the other hand; if you heard this in Europe then its a different set of rules.  I hear from a friend in London the regulatory authorities (such as National Air Traffic Services in the UK) allow the airlines to only use certian numbers at any one time and they often add a bunch of letters to the end just so they can't get the flights mixed up.

And also,

Using different IATA (passenger/luggage) and ICAO (flightplans/atc) flight numbers rarely happens in north america, but is a common occurrence with European airlines....

From this book:

In order to reduce the possibility of two callsigns on one frequency at any time sounding too similar, a number of airlines, particularly in Europe, have started using alphanumeric callsigns that are not based on flight numbers.

Also see the answers here, here and here

"Rare occournance" isn't frequently seen, but it's verbatim :-)

Differing flight numbers and ATC call signs are to avoid having two flights with similar call signs in the area at the same time.  In theory.
In practice, it doesn't really work as well as it does on paper.  Many similar flights are missed and fly together anyway, and the different call signs are confusing in themselves.
We usually brief a different ATC call sign as a threat in our preflight briefing.  Most pilots I've flown with are of the opinion that they cause more problems than they solve.

IATA is used in the ticketing agent world. ICAO is used in air traffic control. The IATA flight number is the ticketing and marketing flight number. When in Air traffic control, there might be through flight, with different aircraft or some other reason the airline can't have the flight number active at the same time, so the airline will then assign a letter or some other reason to make that flight number unique in the ATC system. British Airways does it a lot as well for their international flights.

authors: مختار عبدالوارث


text:
Is LPV considered a precision approach?
WAAS LPV approaches can have decision altitudes as low as 200 AGL, the same as many Cat I ILS approaches. Previous opinions on the Internet have quoted the FAA as saying LPV is considered a non-precision approach, but many of these entries were made more than seven years ago, when the technology was much less mature. Does anyone know if this is still the FAA's position, and are there any RECENT references to their position?

LPV, LNAV/VNAV, and Baro VNAV are considered to be an 'Approach with Vertical Guidance (APV)'. These types of approaches are differentiated from 'Precision' approaches (ILS, PAR, etc.) in the FAA AIM (Section 5-4-5, Paragraph 7):

(b) Approach with Vertical Guidance (APV). An instrument approach based on a navigation system that is not required to meet the precision approach standards of ICAO Annex 10 but provides course and glidepath deviation information. For example, Baro−VNAV, LDA with glidepath, LNAV/VNAV and LPV are APV approaches.

The question has become redundant. ICAO never did like the term ‘APV’ (which as defined logically ought to have included ILS but didn’t) or ‘non-precision’. As of now, in UK at least, it’s correct to refer only to two operational approach methods, 3D - of varying precision, from ILS CAT IIIB to LNAV/VNAV with RNP0.3 to ‘overlay’ NDB - and 2D approaches where vertical guidance isn’t presented to the pilot.

This still comes up in current CAA examinations. I actually came across this thread looking for answers to this question for my upcoming exam.

From the Helicopter ATP PTS (Didn't look at FW):
C. TASK: PRECISION INSTRUMENT APPROACHES
REFERENCES: Part 61; AC 61-27; Pilot's Operating Handbook, RFM, AIM; Instrument Approach Procedure Charts.
NOTE: Two precision approaches must be accomplished in actual or simulated instrument conditions.
NOTE: If the installed equipment and data base is current and qualified for IFR flight and LPV approaches, an LPV approach can be flown to demonstrate precision approach proficiency if the LPV DA is equal to or less than 300 feet HAT.

Can you be a little more specific and try to explain your reference for the benefit of everyone?  I get the gist, but you still should draw a conclusion with your answer.

An LPV approach is in a category by itself. IAW the AIM it is considered an APV or approach with vertical guidance. It "may" not meet the requirements of ICAO 10 precision approach requirements, but does in fact have a Decision Altitude.

Just curious, how does this answer differ from this one from 2014?


text:
Why do most aerobatic aircraft have conventional landing gear?
I was browsing images of aerobatic aircraft on Google and noticed that the vast majority of them have conventional "tail-dragger" landing gear.
Is there any practical reason why this is the case, or rather an aesthetic preference?

Don't have time for research atm, but my guess would be because a tricycle arrangement adds weight/shifts the CoG forward. an acrobatic airframe will most likely have a more powerful engine (read: bigger) already, and there might not actually be any room for a gear. Take the Mustang or Thunderbolt, their front ends were all engine and arms. I'm sure someone will post a correct answer, however.

@CGCampbell: Aerobatic aircraft mostly have fixed landing gears, so space is not an issue. But weight is most likely the correct reason. And drag, since they are fixed gears.

@CGCampbell 1 nose gear may not be able to support the larger engine?

The answer to your question is here.

Pilots w/ large test****s and egos are prone to fly aerobatics and also are prone to fly the non-optimal configuration known as "conventional" or "tailwheel" landing gear.

The tailwheel is much lighter and smaller than a nose wheel. That means reducing airplane overall weight and drag (because the landing gear is usually fixed). And it's probably cheaper, too.

That’s an interesting question. We are students majoring in aeronautics at the University of Stuttgart in Germany. We’re not absolutely sure what the benefit of a taildragger is, but we have a few ideas.
Most aircraft have tricycle landing gear, probably because it’s easier to handle during take off and landing (it doesn’t matter in the air). It’s hard to maintain a straight line on the runway.
However, the taildragger offers one the opportunity to save some weight and to reduce drag. We haven’t seen any research about it, but it is obvious that you can save a little weight because nose gear would be heavier and produce more drag. The nose gear has to be more robust for hard landings.
Another point could be that you want to place a little more weight aft because the engine is one of the heaviest parts and it’s in the nose. You have to balance the weight of the aircraft with the engine to maintain the center of gravity.

A tricycle landing gear does matter in the air: Even retracted, when it does not contribute to drag directly, it adds considerably more mass. Aerobatic aircraft strive for the best thrust/weight ratio, so it does matter. A tricycle gear is only superior if a high wing loading means high landing speed and the requirement to brake the aircraft. Aerobatic aircraft don't need that. For them the taildragger is clearly the better choice.

Taildraggers are lighter and help with saving weight. But the primary reason is because of their symmetrical airfoils. Aerobatic planes have symmetrical airfoils because it acts the same way inverted as it does regularly. This allows the pilot to do inverted flying easier. However, symmetrical airfoils don't actually produce any lift at at a 0-degree angle of attack (going straight into the wind). They need to have a positive angle of attack for this to occur. A taildragger accomplishes this by angling the whole fuselage and, in turn, the airfoil, so that it can still generate lift on takeoff.

Welcome to Aviation.se.  This doesn't really seem to answer the question unless you have some evidence that taildragger aircraft are more likely to have symmetric airfoils, which I don't think is the case.

Do you maybe have a source to support the takeoff claim? A normal tricycle landing gear can also produce the needed AOA during takeoff by rotating the aircraft around the pitch axis like in any normal tricycle landing gear takeoff.

Fighter jets and related trainers outnumber (and outperform) light aerobatic aircraft, they all use tricycle gear.
Most aircraft were tail draggers until after WWII, so it's really an issue of the aircraft design dates to a period when everything had conventional gear. There are no particular advantages to it, but an airframe cannot be converted from one to the other (the balance would be off) so if you want a classic aerobat you also get the classic landing gear.

Zivko Edge 540 and Extra 300 are both new designs. Almost all aircraft had tricycle landing gear when they were designed. Yet they were designed as taildraggers. It is for a reason.


text:
Is it possible for a modern commercial airliner to stop being tracked without substantial mechanical failure?
I was speaking to someone about the MH370 incident, and they suggested that a hijacker could turn off the device that sends the plane's current position, resulting in the appearance of a catastrophic midair failure.
I assume that such functionality could not be turned off, but I could be wrong. Is there any way that this could be done? Could an aircraft's internal tracking systems be "turned off" midair, and also not be located by external tracking like radar?

It's not your question, but even if what you propose is possible then it seems unlikely for such a large aircraft, if it were commandeered and rendered untraceable, to land at an airfield capable of accommodating it without drawing attention. Also, anyone commandeering such a high profile aircraft would likely want to draw public attention, an indispensable element of today's attacks. Nobody's (yet) claimed resp. for attacking the aircraft in question which, when coupled with reports it attempted to RTB, lends credence to either a catastrophic mech. failure or mech. failure & pilot error.

@cfx Yep. Another issue is that the moment the plane lands, or even gets close to landing, mobile phones would likely get some signal and people would be sending messages.

The transponder can be turned off at any time by anyone with access to the cockpit. You can also change the code on a transponder to any value. For example, you could change your code to match that of another aircraft so there was no way to tell the difference between them. You can also put the transponder on standby, so that it is on, but not transmitting.

Related: http://aviation.stackexchange.com/q/2278/193

The device you are talking about is called a transponder.  This is a device that listens for a signal (an interrogation) and responds with information about the airplane including an ATC assigned code, altitude information and additional aircraft info for certain equipment.
There are 2 ways ATC watches airplanes:

Primary Radar
Secondary Surveillance Radar

The transponder is interrogated by the Secondary radar and the response is listened for.  Even with no transponder, the aircraft can still be tracked by primary radar.  This is just a normal radar that is good at seeing airplane sized objects and not so great at seeing weather and can occasionally spot a large flock of birds.  The primary radar is what provides the "blip" on radar and tracks the airplane.  The datablock ATC has on the airplane comes from the secondary, so what ATC will see is a blip with no information.  Turning off the transponder is as simple as setting it to OFF or pulling a circuit breaker and yes, it can be selected OFF in flight, it is just a switch.
The problem with radar is that it only works so far from a radar transmitter and the further away you are the higher you must be to be seen by the radar.  Over the ocean away from land, you are going to be on the fringe of radar or out of radar contact completely and thus unable to be tracked directly by ATC (at this point, non-radar procedures such as position reporting and ETAs can be used to track positions).
The flight in question was apparently visible by a military radar before it disappeared from the scopes (it allegedly observed what appeared to be a turn back toward its origin).

That's amazing, I figured a vehicle of that size would surely have something like GPS hardwired into its operations. From my layman perspective regarding aviation, looks like this'll be a bit of a kick in the pants in regards to airplane tracking. Are there easy avenues to improve it? Or is something like GPS not so accessible to planes?

Even better, many commercial radars aren't even radars as such, they're just displays that show the location information sent out by transponders. Or if they do have an actual radar, it's usually turned off to prevent cluttering the displays with spurious information like flocks of migratory birds.

@andrewb GPS is available but currently not commonly used by traffic control, blame legacy aircraft for that: you'd have to refit thousands of aircraft with a GPS, and that can then also be turned off

@ratchetfreak GPS+Sattelite phone connection in a closed box somewhere out of reach during flight couldn't be at least turned of during flight. Hearing about the incident I, like andrewb, was similarly amazed, but remembered a talk about how airplane soft and hardware are 20 years out of date (stability over security and development) and I guess it makes sense from that point of view.

@andrewb There are other ways that an airplane transmits it's location, both to ATC and to their company headquarters for flight tracking purposes. Many (especially newer) aircraft do have GPS that automatically transmits the position, however the communication system can be turned off if you know how....

@DavidMulder Virtually everything on an airplane can hire turned off, it's just a matter of how. There are circuit breakers designed to protect the system that can be pulled, or even just turn off the batteries and generators for the entire airplane....

@Lnafziger: Still, looking at it as a developer (and security developer) it seems... quite an obvious thing to add a self contained GPS+Sattelite phone+Battery. By default it will be connected to the power source, in case the power source fails it would switch to the battery. Additionally it would be connected to a couple of external sensors (which could probably be turned of with the right know how), still it sounds similar to programming where an error handling routine will not be dependent on any routines in the main program.

@DavidMulder The main problem in an airplane is that it needs to be designed for when things go wrong. What happens if there is an electrical short which causes a fire?  What about a malfunction that causes electrical interference with other systems?  They both happen.  There needs to be a way to turn it off in cases like these in order to protect the aircraft in a "worst case scenario" for the electronic component.

@Lnafziger: Can't remember last time my phone (or any phone) burst out into flames. And it's practically the same hardware (different chip for the transmission, but even that one isn't drawing enough power to cause such a short if designed correctly). And it's not like interference will magically manifest itself during a flight. Of course you would have to test it, and for sure there are procedures how to do those tests, but it's not without a reason that on the software side airplanes are a terrible mess. And solving them with the mindset you describe is never gonna happen.

@DavidMulder I'm with Lnafziger on this one; any thing powered needs a fuse (all accessible behind the captain), adding a battery just adds the risk of it leaking/exploding due to overcurrent cause be faulty wire somewhere else and damaging other things

@Both of you: You gotta be kidding me, I am quite the privacy advocate, but whoever came up with the idea that the user (pilot) should be in control over those kind of things with aircrafts... It's RIDICULOUS that in the modern age we don't know +- 15m where a crash happened. Or that any consideration can be given to an airplane getting hijacked/stolen. I mean, as far as I care you may put that phone (which it boils down to being) into a second black box with just the antenna and main power coming from the outside, but this reminds me of http://xkcd.com/463/

@DavidMulder Yes, interference can just "magically manifest itself during a flight" when a component on a circuit board fails. Electrical wiring or pretty much any component on a circuit board can fail and create a hazard. That's why almost everything is protected with independent systems so that you don't lose the entire electrical system just because the sat phone shorted out. I'm not talking about the software side of things, just basic electrical hardware protection design. I'm a pilot who happens to be an electrical engineer. Let me assure you that it isn't as simple as you think.

@DavidMulder - Perhaps you recall the 787 recall that happened a few months back?  Faulty lithium ion batteries that started a fire, same batteries as what you see on a cell phone...  Look, nobody is saying you are wrong, we all know it ought to be done.  It's just about 100 times harder to do on an airplane than it is to do in consumer electronics.  There is a failure rate with consume electronics, companies have whole entire tech supports to fix their customers problems, and that's fine.  But an airplane...a failure just makes the plane crash, so designers have to be very very very careful.

@DavidMulder: While my phone never burst into flames, I certainly do remember handful of cases where electronic items did, including one relatively recent where camera just burst into flames in someone's hand luggage.

@DavidMulder This conversation has gone far enough as a comment thread and is not what comments are designed for. If you have an interest in more information about this topic, please ask your own question where we can offer full answers (with formatting, pictures, and hyperlinks) to better address your question/concerns and get different feedback from different people.  You are also welcome to drop by [chat] if you just want to talk about it with other people in the industry. I understand your point of view, but there are technical reasons why things are the way that they are on airplanes.

and if the pilot knows the area and terrain, he can always reduce altitude and use terrain masking (of course in populated areas that'd lead to visual detection and people calling the police).

The JACC confirmed in an interview between Sir Angus Houston and the Malaysian Chronicle on 24 June 2014 that MH370 was not seen on radar climbing to 45,000ft nor turning west and diving to low altitude. There was no such radar data.

With the proper knowledge of the aircraft systems almost anything can be turned off.  That's what we do at the end of almost every flight day.  Most of the communications systems can actually be turned off fairly easily, but the average person would not know how to do it.
In airplanes like the 777, there are multiple ways that they communicate but all of them can be turned off (transponders, ACARS reports, CPDLC, ADS-B, radios, satellite phones, etc.).  Some are automatic and some are manual,  and not all aircraft have all of them.  Most of them have a switch or can be controlled through the Flight Management System, but the ones that don't will have a circuit breaker designed to protect the system which may be pulled in order to deactivate the system.

As a B-737 pilot, I can tell you that ALL electrical components are wired into the electrical system to a specific electrical BUS. It would not be hard to determine which BUS(S) run power to the associated component and therefore knowing which circuit breaker(s) to pull. The ACARS that transmits our FOQA information can be disconnected on the BBJ I fly. I assume it can be done in the B-777.

Not only that, I assume that you can just turn off the satellite and VHF data communication directly from your FMS.  (At least I can on my airplane!)

Yes. I provided the information in my answer:  https://aviation.stackexchange.com/a/7787/22550

With today's locked cockpit policy it is extremely unlikely that hijackers would be able to turn off the transponder without pilots being able to set it to 7500, the code for unlawful interference, for at least a short while. Because while the transponder can be turned off, the hijackers would have to get into the cockpit first.
The cockpit door can't be opened from cabin side. Even if the stronger code is entered that will open the door (for cases when one pilot is incapacitated while the other is in the lavatory) the pilots still have some time to cancel the unlock request. Therefore the hijackers would have to threaten with something to get the pilots unlock, but that would give the pilots time to provide some indication of the hijack to the ATC.

Setting the transponder to 7500 when out of radar range won't help.

Also clever social manipulation combined with poor pilot practices could get you in there. There's also the possibility that a pilot could be in on it.

Had another quick look at the news and it turns out the pilot has a history of letting people into the cockpit! http://www.theguardian.com/world/2014/mar/11/malaysian-flight-mh370-copilot-teenagers-fariq-abdul-hamid

@andrewb: Interesting...

« With today's locked cockpit policy »? I succeeded to enter a 747 cockpit last year during the flight (end of cruise and begin of descent). Just needed to smile to the purser and say "I'm PPL". But it will depend of course on the airline, and the current crew.

re: "Setting the transponder to 7500 when out of radar range won't help." – MH370 was not out of radar range when it was diverted.

Another Boeing 777 on 12th July 2014 suffered smoke in the cockpit and cascading loss of electrical systems, navigation displays and Comms in the cockpit. That was Continental Flight 201 which made an emergency landing on Midway island.
There are disputed claims that flight 201's transponder also failed during the emergency.
In the case of MH370 it is acknowledged that the ACARS suffered a power interruption prior to log-on requests. It seems possible that the transponder was affected by whatever power interruption the ACARS suffered therefore it is not an automatic assumption that the transponder and ACARS were turned off deliberately.

With Continental Flight 201, did they lose all transponder capabilities?

"radar data indicate the transponder worked until touchdown." - Aviation Herald

The plane's position is reported by ACARS and by the transponder.
MH370 lost ...

... its Mode S transponder (shortly before 17:20:33 UTC)
... ACARS (somewhere between 17:07:49 - 17:37:29 UTC)
... and the SDU (somewhere between 17:07:49 - 17:37:29 UTC).
The SDU was repowered, however, at 18:25:27 UTC, when it logged onto the
Inmarsat satellite network again.

The first 2 items can be easily disabled in the cockpit.
The SDU can be disabled by either turning off the AES circuit breaker in the E&E bay or depowering the left main AC bus in the cockpit (which results in the collateral loss of various systems).
India has made it mandatory for aircraft flown by Indian operators to install a device reporting the aircraft's location every 15 minutes, thereby preventing the aircraft from disappearing:

India makes its aircraft disappearance proof post MH370 incident
« India has taken several steps to remove any possibility of the
  aircraft operated by its airlines disappearing without a trace in the
  aftermath of the shocking incident in March 2014 involving Malysia
  Airlines’ MH370. It has made it mandatory for aircraft flown by Indian
  operators having a seating capacity of 19 passengers or takeoff weight
  of 45 tonnes or more to install a devise that will send location of
  the aircraft at 15 minute intervals.
The government had ordered airline companies to compulsorily install
  an automated aircraft tracking system (ATS) in all aircraft
  falling in the above categories. The system will pass location
  information to ground stations even if the aircraft is flying over the
  oceans during long international flights throughout the duration of
  the flight. » (source)

Of course, this only makes the aircraft disappearance-proof if the ATS doesn't happen to fail.


text:
Would in flight engine failure of the passenger jet be reported?
A passenger plane with two or more engines would probably land without big difficulties with one engine inoperative.

Would the passengers be notified, asking to take the brace position during landing?
Would such event have an accident investigation report?
Would this report later be available for general public, as are the reports of various significant air disasters?

losing an engine means diverting to nearest airport and landing there IIRC

@ratchet freak:  Nearest suitable airport.  So some pilot discretion involved.

@ratchetfreak: In 2-engined aircraft yes (and emergency shall be declared). 4-engined aircraft may, and often do, continue as permitted by fuel on board.

To certify any Commercial Jet Plane worthy of flying,
a 2 engine plane must be able fly with just 1 engine running
a 3 engine jet like the Lockheed L1011 or DC10 with just 1
a 4 engine jet with just 2. Although not a requirement, the 747, A380  could fly on one engine but are not be able to maintain the cruise altitude indefinitely and will eventually become  long-range gliders so they must land immediately.
The landing approach and procedures vary on how much the plane weighs prior to landing.

Would the passengers be notified, asking to take the brace position during landing?
Brace Positions are only assumed on impact emergencies, like crash landings. Losing an engine doesn't mean you are going to crash so no brace will be assumed.
Would such event have an accident investigation report?
There will be an investigation but if the plane landed safely it wont be filed as an accident. The plane plus the engines passed its FAA, EASA, etc Certification so it may be a number of reasons why the engine malfunctioned, like bad maintenance, faulty parts etc.
This is an extract from wikepedia -- http://en.wikipedia.org/wiki/Turbine_engine_failure

Shut downs that are not engine failures
Most in-flight shutdowns are harmless and likely to go unnoticed by
  passengers. For example, it may be prudent for the flight crew to shut
  down an engine and perform a precautionary landing in the event of a
  low oil pressure or high oil temperature warning in the cockpit.
However, passengers may become quite alarmed by other engine events
  such as a compressor surge — a malfunction that is typified by loud
  bangs and even flames from the engine’s inlet and tailpipe. A
  compressor surge is a disruption of the airflow through a gas turbine
  engine that can be caused by engine deterioration, a crosswind over
  the engine’s inlet, ingestion of foreign material, or an internal
  component failure such as a broken blade. While this situation can be
  alarming, the condition is momentary and not dangerous.
Other events such as a fuel control fault can result in excess fuel in the engine’s
  combustor. This additional fuel can result in flames extending from
  the engine’s exhaust pipe. As alarming as this would appear, at no
  time is the engine itself actually on fire. Also, the failure of
  certain components in the engine may result in a release of oil into
  bleed air that can cause an odor or oily mist in the cabin. This is
  known as a fume event. The dangers of fume events are the subject of
  debate in both aviation and medicine.

Would this report later be available for general public, as are the reports of various significant air disasters?
It depends, as you read above the flight deck crew may shut down an engine because of low oil pressure. Would that have significance of becoming public knowledge?
However as an example, if the problem of an engine failure escalates to the manufacturer then the airline may ground the fleet and that then becomes public knowledge and the reason why because the airliner would give media statements.
It all depends on the severity of the problem. Like this one that got reported --- http://www.b737.org.uk/accident_reports.htm

20 August 2007; B-18616, 737-800, 30175/1182, FF 11 Jul 02, Okinawa,
  Japan:
Engine #1 caught fire shortly after docking destroying the aircraft.
  No fatalities. The cause was the detachment of a slat pylon bolt which
  fell off and pierced the fuel tank which leaked and ignited. According
  to the JTSB the washer that should have held the nut in place probably
  detached during maintenance 6 weeks before the incident. The design of
  the nut has since been changed to limit the likelihood of detachment.

Engine shut-down is always a serious incident and as such it should be investigated and the record published (depending on the thoroughness of the overseeing authority some may fall through the cracks). They are not often run through media, but you can find them in bulletins published by the relevant authorities. Representative selection is also published on The Aviation Herald

1) "would probably land without difficulty" - you have it right there.  If there are no other complications, there would be no need to have the pax assume the brace position.
2) You may regard this as semantics, but an engine failure followed by a normal landing does not meet the FAA definition of an accident.  Would it be reported to the airline maintenance folks and the FAA as a matter of routine?  Of course.
3) See #2.  Since the scenario as presented doesn't rise to the level of an accident, there will be no accident report.  This does not rise to the level of a "significant air disaster."
Having said that, there are many ways an engine-out situation can lead to an accident with severe consequences.  Then the reports will be flying! (Pun intended...)  Google 'Captain Al Haynes United Flight 232' for one example.

UA 232 was one hell of a flight. But that was an all engines out scenario. @OP, check out BA Flight 9.

@shortstheory:  That is incorrect.  The DC-10 had a single uncontained engine failure that destroyed all hydraulic systems rendering all flight controls inoperative.  Using differential thrust on the remaining engines allowed the crew to bring the plane down to a crash landing on the runway so that many survived.

Single engine inoperative scenario? China Airlines 006

@SkipMiller, yes, that is correct. I'm sorry I must have mixed it up with another crash at the time of commenting.

It does not meet definition of accident, but it does meet definition of significant incident and those are investigated as well. The report will be usually brief (often just paragraph in a summary bulletin), but NTSB (not FAA) (or appropriate agency in other countries) will at least want to review the maintenance log to check for potential systemic or recurring problems.

@JanHudec:  What is the definition of "significant incident"?  I thought this was a three tier system: accident, incident, and normal ops/wear and tear.  You are implying it is a four tier system and I would like to learn about that.

@SkipMiller: Oops, sorry, "serious incident". I don't know the exact definition, but there appear to be three sub-tiers in incident. The most serious is "serious incident", which gets separate investigation. While the lower severities are only noted and further action is only taken if the problem is recurrent.

Would the passengers be notified, asking to take the brace position during landing?

If the aircraft is going to divert, and in most cases it is1, it's not possible to avoid passengers noticing. They will not be asked to assume brace position though, because the landing will be mostly normal on runway with properly deployed landing gear.

Would such event have an accident investigation report?

It will have incident or accident investigation report.
Accident is defined as occurence causing death, injury or significant damage to the aircraft except engines or gear. So most engine failures won't be qualified as accidents (including some uncontained failures).
They will however be qualified as serious incidents2 and those are investigated as well. Reports of such incidents are usually brief, often just paragraph in summary bulletin, but the overseeing authority (in USA that's NTSB) will usually at least want to carefully review the maintenance findings and logs to check for potential signs of systemic or recurring problem.

Would this report later be available for general public, as are the reports of various significant air disasters?

They should be.
These incidents rarely appear in mainstream media, but The Aviation Herald has a representative selection3 of them or you can go to the various sites of the relevant authorities. Authority overseeing the engine manufacturer will usually be involved, so NTSB (USA), AAIB (UK), BEA (France) and MAK (Russia/CIS) will probably cover most, or at least most of the notable, of the incidents.
1In a 2-engine aircraft engine out is always emergency and requires landing at nearest suitable airport. In aircraft with more engines the flight may be continued but with less thrust the aircraft has to drift to lower flight level and the fuel burn is higher and the flight often has to divert due to fuel shortage (it is not emergency, so it does not warrant using the required fuel reserves).
2Incidents are rated in several classes. The most severe is class is called "serious incident" and each instance of serious incident gets it's own investigation.
3Not all, because some authorities are more thorough than other, so the respective countries would look worse when they are actually safer. Explained in this article, but unfortunately it has no anchors to make direct link. Search for "percent of all daily occurrences". Canadian TSB is mentioned as most thorough.


text:
What does it take to enter the Red Bull Air Race?
Starting from being a newly minted private pilot, what are the steps I would have to accomplish in order to eventually qualify for and compete in the Red Bull Air Race? Assuming I put most of my time into the endeavour and progressed at a reasonably fast pace, how long would it take me?

I'd probably start with 10,000 hours and a correspondingly large sum of money.

Not to mention balls of absolute steel.

I've voted to close for too broad. An answer to the title question has been given by @Jamiec. However, in the body, the OP states he wants to know the process starting from the time the new pilot has just received their PPL. The steps to go from that point to one of, if not the, single most intensive and challenging air race there is would simply be unanswerable in any meaningful way in this forum.

@CGCampbell - FWIW I totally agree this is too broad.

According to their about page

New pilots who wish to participate in the World Championship must first fulfil the minimum criteria set by the Red Bull Air Race Committee, which include top achievements in international flying competitions organised by the FAI. They must also be active aerobatic air display pilots. Eligible pilots that prove their skills at the Red Bull Air Race Qualification Camp can achieve the Red Bull Air Race Restricted Superlicence. Once they have the Restricted Superlicence, they then qualify to take part in the Red Bull Air Race World Championship in the Challenger Cup.

So I would suggest if this is something that interests you, you begin with some instruction in aerobatic flying - a discipline which in itself is quite tough. To find the next qualification camp, I would suggest contacting red bull air race directly. It seems they run annual qualifications, most recently held in Texas, USA.
The amount of time it would take is impossible to measure, or even speculate.


text:
How much fuel do the new A320-Winglets burn vs. the B737-800?
Now that the new A320-Winglets have established themselves, I'm wondering if they have better fuel consumption than the B737-800?
I was told that Boeing used to be marginally better. Is that still the case?

I'd suspect that this is quite dependent on the mission -- there's a reason not everyone is grabbing these new A320s. Not sure how to change this question though. From memory each still has a block fuel burn advantage at different stage lengths, with the Boeing being better at shorter distances and vice versa.

@Qantas94Heavy there are other reasons besides marginal differences in fuel consumption for sticking with what you have :)

@jwenting: true, though there have been cases of airlines switching sides because of their changing needs.

@Qantas94Heavy yes, but you'd not replace a 737-800NG with an A320NG. It's way too new. A 737-300 would be a suitable candidate.

Winglets do not "burn" or "consume" fuel.  They just reduce fuel consumption of the parts that do.

Airbus says this about their new blended winglets (aka "Sharklets"), being fitted to new A320s, and retrofitted:

Airbus’ next step is the large Sharklets™ wingtip devices, representing another element in the ongoing continuous improvement programme for its best-selling A320 Family. These devices improve aerodynamics, reducing fuel burn by up to 4 per cent – which amounts to annual savings of more than 900 tonnes of CO2 per aircraft.

Given that an A320's fuel burn rate is approximately 5.13 gallons per seat per hour, reducing this by 4% gives you 4.92 gallons/seat/hr.
Comparatively, a 737-800 burns about 4.88 gallons/seat/hr.
Source:

A 737-800 burns 4.88 gallons of fuel per seat per hour, compared with the comparable A320's burn of 5.13 gallons per seat per hour, according to The Airline Monitor, an industry publication.

So they're near enough the same.

consumption per seat per hour? Now I'm curious. It seems both consumption per hour and commercial speed are similar, so consumption per kilometer must be the same?

Pretty much, correct.

The 737 MAX is more fuel efficient than the A320ceo. The A320neo, however, has marginally better range and fuel efficiency than the 737 MAX, but it is not in production yet.

citations? numbers?

Um, neither the A320neo nor the 737 MAX are in production yet.


text:
Is the descent performance of the PMDG 737-800 accurate?
I often fly the PMDG 737-800 (with winglets) in my home simulator and most of the time, I find it hard to slow the aircraft down for landing when I descend. Most of the time, I need to deploy the speedbrakes to keep descending without increasing speed. I usually start my descent earlier than the marked top of descent point to make the flight a little smoother.
So I was wondering if this is a bug or if the real aircraft actually behaves like this. I have wondered about this for some time. I can only dream about becoming a pilot and find out myself cause of my bad eyesight.
Here is a video on YouTube of me landing the 737 where I had to deploy speedbrakes.
Since this video is getting a little outdated: I can no longer recall exactly the payload or weight of this aircraft. But I normally fly with a heavy payload.

The "willingness" of the aircraft to descend depends on a few factors, including weather conditions, aircraft weight, your speed and the resulting rate of descent. You might want to add those specifics so we can see whether that would compare with a real-world aircraft or not.

I actually have a video of me landing the PMDG in Heathrow, London. It can be found here: http://www.youtube.com/watch?v=8BGL5lH-VXY
About the weight, wind and weather factors: I am not sure as it differs a lot. I usually let FSX choose a random payload before each flight. And the weather and wind is not always the same. The video might show some of it.
I know i did mistakes during that landing (like using the anti-ice or doing a "clean-up" on the runway). So please don't point at those if it doesn't play a factor about this subject.

According to "Pilot_H" on Twitch, who is a Ryanair 737-8 pilot and regularly streams the PMDG 737 in P3D/FSX, the PMDG performs very similarly to the actual aircraft in almost every phase of the flight.

You haven't provided everything possible to really ascertain the issue noted, but based on what you have I've noticed the following things:

You'll find most 737s at 240-250 KIAS passing through 10000 feet, rather than the 220 knots that you were going at (while 220 KIAS is above minimum clean speed at normal landing weights, it's still slower than most)
Being heavy actually makes minimum drag and max L/D speeds higher, which means that for the same speed, you'll actually descend at less of a gradient than if you were lighter
The Boeing 737-800W has a idle descent ratio of about 1:20, which means that at 250 knots you're only going to be descending about 1200fpm -- the 737-800 (especially with winglets) is a very slick bird.

For your reference, you can see the distances required for an idle descent (.78/280/250), plus allowances for a straight-in approach:
|=====================================================|
|          |       |      |       DISTANCE (NM)       |
| PRESSURE |       |      |---------------------------|
| ALTITUDE | TIME  | FUEL |  LANDING WEIGHT (1000 KG) |
|   (FT)   | (MIN) | (KG) |  40  |  50  |  60  |  70  |
|----------|-------|------|------|------|------|------|
|   41000  |   27  |  340 |  102 |  119 | 133  |  142 |
|   39000  |   26  |  340 |   97 |  114 | 127  |  136 |
|   37000  |   25  |  330 |   92 |  108 | 121  |  130 |
|   35000  |   24  |  330 |   88 |  103 | 116  |  125 |
|   33000  |   24  |  320 |   84 |   99 | 111  |  120 |
|   31000  |   23  |  320 |   80 |   94 | 105  |  113 |
|   29000  |   22  |  310 |   75 |   88 |  98  |  106 |
|   27000  |   21  |  300 |   70 |   82 |  92  |   99 |
|   25000  |   20  |  300 |   66 |   77 |  86  |   92 |
|   23000  |   19  |  290 |   61 |   71 |  79  |   85 |
|   21000  |   18  |  280 |   57 |   66 |  73  |   78 |
|   19000  |   17  |  270 |   52 |   61 |  67  |   72 |
|   17000  |   15  |  250 |   48 |   55 |  61  |   65 |
|   15000  |   14  |  240 |   44 |   50 |  55  |   58 |
|   10000  |   11  |  200 |   30 |   34 |  37  |   39 |
|    5000  |    7  |  150 |   18 |   19 |  20  |   21 |
|    1500  |    4  |  110 |    9 |    9 |   9  |    9 |
|=====================================================|

I like the table. Could you cite the source for it?

@BretCopeland: some oldish internet FCOM, not exactly legitimately sourced.

Are these for a fixed IAS or a fixed angle-of-attack?  What is the meaning of "(.78/280/250)"?  This answer would be made much more useful to some of us non-airline-pilots if the meaning of ".78/280/250" were clearly explained.

Until someone with more authority steps in...
I have a friend who flies 737's and he has mentioned several times how well they glide and how difficult they are to slow down. He tries really hard to not to use the speedbrakes because "they just shake the plane" making an uncomfortable experience for the passengers. They simply manage this "problem" (actually a really good thing in terms of fuel burn) by planning the descent properly, and always starting down early enough to not require spoilers.
I can't speak as to the accuracy of PMDG, but I would guess the performance you're seeing is at least roughly similar to real world, and it's your descent planning which needs adjusting. What surprises me is that the FMS wouldn't automatically select a reasonable top of descent, but perhaps there is a difference between how you are flying the descent and how the FMS expected it to be flown.

I have not flown the 737, but I can tell you that jets in general have a relatively low amount of drag (they are very "clean").  This makes them hard to slow down and they build up speed easily and quickly.  The 737-800 is a Next Generation 737, and has the updated wing that includes (among other enhancements) winglets, so this problem would be even more prevalent than on the classic 737's.
Slowing down and going down at the same time is very hard to do in airplanes like this, and use of spoilers is almost always required when the airplane is in a clean configuration if you need to do both.  Descent planning is an important part of flight in such aircraft.

I fly now with Prosim and the Prosim Flight Model. Before I  jused PMDG and I also had a difficult time with bleeding the speed off during decsent. Almost everytime I got to high and too fast on visual approach to my home airport using real VFR-routes and descent-paths.
Free speed descents" which the airliners get from ATC every now and then was never sucsessful.
But with the prosim flightmodel I experience alot more sucsess on descent. It's much more realistic drag simulation in my opinion. Fuel usage is spot on and climb performance are spot on. So I dont think there is too much drag either..


text:
Where exactly are the pitot tubes positioned on the A330/340?
While going through a document for analysis I came across a statement saying the positions 1 and 2 of the pitot probes are symmetrical on long-range Airbus aircraft but not on their single-aisle aircraft.
Can any one please confirm it by giving suitable reference? I didn't find any clue on the internet.

Seems like they are under the cockpit for the A330
source
Couldn't really find anything for the A340 that helped with answering your question but I assume based on the A330 that they most likely are located somewhere in the same area.

In FCOM of A320, there is an image on pg 722, Vol 1 called probes location. By visual inspection one can observe a that captain side pitot probe is little above on other side the F/O. But now text  confirmation for this inspection on I found. NO such info about A 330/340 is found.

I got this image from researchgate, so I felt it was trustworthy. Sorry if it doesn't help.

I got the answer for this question.
In one of the documents( cant give , confidential) it is confirmed that Pitot tubes 1 and 2 position are different on LR an SA. They are symmetrically placed on LR. On SA Pitot 2 is placed a little higher than Pitot 1. This is not so significant via visual inspection but plays a role while performing verification of flight test.

You can't even share the title of the document, even if you're not allowed to directly quote the contents?

My college has sent me email from france in snapshots. So, email communication cant share. Policy !

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/